To deliver video, content may be packetized and sent over IP. To ensure that a multimedia network is able to reliably deliver content, spatial diversity may be utilized. For example, two streams from two different points may be injected into the network, e.g., a stream from San Diego and a stream from Atlanta may be injected into the network. Once the traffic is injected into the network, the video is processed for provisioning.
Digital cable services use quadrature amplitude modulation (QAM) modulation. An edge QAM device may carry video-on-demand (VOD) and switched digital video streams as well as Internet Protocol data and voice. Thus, an edge QAM device may be used to select the best stream for routing downstream to customers.
Spatial diversity has been a key design in video delivery mechanisms since the two paths taken by the streams may be maximally disjoint and hence the correlation in their network induced impairment orthogonal or independent. Spatial diversity has proven effective in providing reliable content delivery while attaining minimum cost.
Even though techniques such as the use of special diversity are implemented, video impairments may still occur in a video network for any number of reasons. Impairments may occur in the form of instability in the stream, quality degradation, packets being dropped, etc. For example, video impairments may be induced by either the encoder or the transport network, such that the total distortion at the decoder is the sum of both distortions of the encoder and the network. In other words, Ddec=Denc+DPLR, wherein Ddec is the distortion of the decoder, Denc is the distortion of the encoder and Dpir is the distortion due to network in term of packet loss rate. To meet strict quality of experience requirements for broadcast video over IP, the packet loss rate must be lower bounded by 1×10−6 packet loss. Networks may be designed with the appropriate quality of service (QoS) and MPLS-based protection. However, the impact of packet loss in the transport network has a multiplicative affect at the encoder due to error propagation from reference frame into dependent frame. In other words, Pframe—loss=k×DPLR, such that P( F|I)=1−(1−p)SI, where p is the probability of packet loss and SI is the number of IP packets per I frame assuming that no application layer forward error correction (FEC) and no error concealment at the decoder. Also the probability of decoding error due to a P frame corruption is
            P      ⁡              (                              F            _                    ❘          P                )              =                  1                  N          P                    ⁢              (                                            ∑                              k                =                1                                            N                p                                      ⁢            1                    -                                    (                              1                -                p                            )                                      SI              +              kSp                                      )              ,where Sp is the number of P packets that constitute to a P frame and Np is the number of P frames in a group of pictures (GoP).
For example, Stream A may be the preferred video stream. Stream A may have direct connectivity with the video, e.g., HBO, ESPN, etc. Expensive encoders and decoders may be used on the direct Stream A, thereby avoiding the need to apply too much compression on Stream A. Thus, the quality of the video feed of Stream A is much better than a satellite feed. When the edge QAM device receives the two streams and an event occurs that triggers a switch to Stream B, the provider thereafter maintains the Stream B feed no matter what else happens until somebody is sent to reset it. Thus, to switch back to Stream A, service personnel have to travel to the access point and physically reset it.
Alternatively, the switch may be made, but without any knowledge about the impairments that triggered the switch in the first place. Once Stream A meets predetermined criteria, the edge QAM switches back to Stream A. Still, Stream A may quickly trigger another switch to Stream B. This may occur multiple times resulting in a ping-pong or rapidly switching back and forth between Stream A and Stream B. Dropping an occasional packet does not present a problem because most transmissions use the transmission control protocol (TCP), which probably allows recovery of the dropped packet. In contrast, with video over IP, a lost packet is truly lost when a packet is dropped and quality is dependent on the encoding mechanism and how many packets can be lost without significant degradation.
It can be seen that there is a need for method, apparatus and program storage device for mitigating network impairments on video quality.